1. Field of the Invention
The present invention generally relates to medical devices and methods, and more particularly relates to the treatment of valve insufficiency, such as mitral insufficiency, also referred to as mitral regurgitation. The use of prosthetic valves delivered by traditional surgical implantation methods, or by a less invasive percutaneous catheter or by minimally invasive transapical methods are one possible treatment for valvar insufficiency (also referred to as regurgitation).
The heart of vertebrate animals is divided into four chambers, and is equipped with four valves (the mitral, aortic, pulmonary and tricuspid valves) that ensure that blood pumped by the heart flows in a forward direction through the cardiovascular system. The mitral valve of a healthy heart prevents the backflow of blood from the left ventricle into the left atrium of the heart, and comprises two flexible leaflets (anterior and posterior) that close when the left ventricle contracts. The leaflets are attached to a fibrous annulus, and their free edges are tethered by subvalvular chordae tendineae to papillary muscles in the left ventricle to prevent them from prolapsing into the left atrium during the contraction of the left ventricle.
Various cardiac diseases or degenerative changes may cause dysfunction in any of these portions of the mitral valve apparatus, causing the mitral valve to become abnormally narrowed or dilated, or to allow blood to leak (i.e. regurgitate) from the left ventricle back into the left atrium. Any such impairments compromise cardiac sufficiency, and can be debilitating or life threatening.
Numerous surgical methods and devices have accordingly been developed to treat mitral valve dysfunction, including open-heart surgical techniques for replacing, repairing or re-shaping the native mitral valve apparatus, and the surgical implantation of various prosthetic devices such as annuloplasty rings to modify the anatomy of the native mitral valve. More recently, less invasive transcatheter techniques for the delivery of replacement mitral valve assemblies have been developed. In such techniques, a prosthetic valve is generally mounted in a crimped state on the end of a flexible catheter and advanced through a blood vessel or the body of the patient until the valve reaches the implantation site. The prosthetic valve is then expanded to its functional size at the site of the defective native valve.
While these devices and methods are promising treatments for valvar insufficiency, they can be difficult to deliver and anchor, expensive to manufacture, or may not be indicated for all patients. Some of these prosthetic valves having anchoring mechanisms that secure the valve to various portions of the native valve anatomy. For example, some the valves are anchored to the atrial floor, the valve annulus, a ventricular wall, or to the valve leaflets. However, in some situations, depending on anatomy, skill of the physician, as well as other factors, the prosthetic valve may not always be successfully anchored. For example, in the case of a prosthetic mitral valve with anchors for securing the valve to the native anterior and posterior leaflets, if the anchor(s) do not successfully engage the posterior leaflet, the prosthetic valve may be pushed upward toward the atrium during ventricular contraction due to the force of the blood. This may result in an improperly positioned valve which can prevent the valve from properly functioning. Therefore, it would be desirable to provide improved devices and methods for the treatment of valvar insufficiency such as mitral insufficiency. Such devices and methods preferably have alternative or improved anchoring mechanisms and methods to more securely anchor the prosthesis to the valve structure. At least some of these objectives will be met by the devices and methods disclosed below.
2. Description of the Background Art
By way of example, PCT international patent number PCT/US2008/054410 (published as PCT international publication no. WO2008/103722), the disclosure of which is hereby incorporated by reference, describes a transcatheter mitral valve prosthesis that comprises a resilient ring, a plurality of leaflet membranes mounted with respect to the ring so as to permit blood flow therethrough in one direction, and a plurality of tissue-engaging positioning elements movably mounted with respect to the ring and dimensioned to grip the anatomical structure of the heart valve annulus, heart valve leaflets, and/or heart wall. Each of the positioning elements defines respective proximal, intermediate, and distal tissue engaging regions cooperatively configured and dimensioned to simultaneously engage separate corresponding areas of the tissue of an anatomical structure, and may include respective first, second, and third elongate tissue-piercing elements. The valve prosthesis may also include a skirt mounted with respect to the resilient ring for sealing a periphery of the valve prosthesis against a reverse flow of blood around the valve prosthesis.
PCT international patent number PCT/US2009/041754 (published as PCT international publication No. WO2009/134701), the disclosure of which is hereby incorporated by reference, describes a prosthetic mitral valve assembly that comprises an anchor or outer support frame with a flared upper end and a tapered portion to fit the contours of the native mitral valve, and a tissue-based one-way valve mounted therein. The assembly is adapted to expand radially outwardly and into contact with the native heart tissue to create a pressure fit, and further includes tension members anchoring the leaflets of the valve assembly to a suitable location on the heart to function as prosthetic chordae tendineae.
Also known are prosthetic mitral valve assemblies that utilize a claw structure for attachment of the prosthesis to the heart (see, for example, U.S. patent publication no. US2007/0016286 to Hermann et al., the disclosure of which is hereby incorporated by reference), as are prosthetic mitral valve assemblies that rely on the application of axial rather than radial clamping forces to facilitate the self-positioning and self-anchoring of the prosthesis with respect to the native anatomical structure.
Another method which has been proposed as a treatment of mitral valve regurgitation is the surgical bow tie method, which recently has been adapted into a minimally invasive catheter based treatment where an implant is used to clip the valve leaflets together. This procedure is more fully disclosed in the scientific and patent literature, such as in U.S. Pat. No. 6,629,534 to St. Goar et al., the entire contents of which are incorporated herein by reference.
Other relevant publications include U.S. Patent Publication No. 2011/0015731 to Carpentier et al. and WO2011/137531 to Lane et al. While some of these devices and methods are promising, there still is a need for improved devices and methods that will further allow more accurate positioning of a prosthetic valve and that will also more securely anchor the valve in place. At least some of these objectives will be met by the exemplary embodiments disclosed herein.